The Great Labor Day Mosquito Count

Results from the 2004 sampling effort: 

(summary of progress as of June, 2005)

We have completed the processing for most of the sites.  Some are still underway, but the sites that are most relevant to the expansion of the range of the invading species Aedes albopictus have been done. 

There are various ways of looking at the data.  For simplicity here, we have concentrated on "mean crowding," which is like mean density (average individuals per trap), except that it ignores traps that received no eggs, and instead concentrates on the individual egg's point of view:  how many other individuals are in the trap?  Averaged out over all the eggs, mean crowding tells us how many neighbors the average egg has.  The main advantage of this approach is that it avoids the problems that can arise when students go out and put their traps in places unattractive to mosquitoes.  To see the formula for mean crowding, and a numerical example, click here.  For a table of the results so far, click here

The maps below summarize our findings, superimposed over the previously published (2000) distribution of the invading Aedes albopictus from the CDC.  Click on each for an enlarged view.

Locations of groups who received materials for the Labor Day Mosquito Count
Mean crowding of the native mosquito species, Ochlerotatus triseriatus, obtained from the 2004 Labor Day Mosquito Count
Mean crowding of the invading mosquito species, Aedes albopictus, obtained from the 2004 Labor Day Mosquito Count
Proportions of native (blue) and invading (red) species in samples from the 2004 Labor Day Mosquito Count.
Overall mean crowding, based on data from the 2004 Labor Day Mosquito Count.
The distribution of the invading Aedes albopictus (brown), and places where it has been found in the 2004 Labor Day Mosquito Count
Four new counties added to the known Aedes albopictus distribution, due to the 2004 Labor Day Mosquito Count

New findings

We have found the invading species Aedes albopictus in four counties where it has not been previously reported: 

  • In Maryland, Prince George's County, thanks to Paty Guzman and her students in Riverdale MD
  • In West Virginia:  Brooke County, thanks to Andrea Anderson and her students in Weirton WV, and to Jules Adam, Stephan Smolski and their students in New Cumberland WV; Kanawha County, thanks to Danielle Dyer and students in Charleston WV, and to students of Rachelle Marion in Belle WV; and Fayette County, discovered by students of Wayne Yonkelowitz of Fayetteville WV.
  • In Wisconsin, thanks to Barb Kingsbury and her students in Loyal, we may have a new distribution record for Aedes albopictus, which has never even been seen in the state before.  We're working to verify this one using amplification of DNA sequences, and are doing the same with some eggs from Rhode Island (collected by students of Mary McCarthy in Riverside RI and surrounding towns)Aedes albopictus has not been found in either of those states; although it seems that it will only be a matter of time for Rhode Island, a positive finding in Wisconsin would be a surprise.
This information will be useful in providing a more complete picture of the course of this invasion, and may also be useful to mosquito control workers with an eye toward the possible threat of this introduced species to human health.

Extremes (high, low density, Northern, southern)

The highest overall abundance of mosquitoes was found in Evans WV (Ravenswood Middle School, Jackson Co.).  Evans also had the highest mean crowding of Aedes albopictus.  The most abundant population of the native eastern treehole was found in Fayetteville WV (Fayette Co.).

Seven sites received no eggs in their traps at all.  These included West Alexandria OH, Hammond IN, Beach Park IL, Clear Lake SD, Junction IL, El Paso TX, and Beckley WV.  Several explanations could account for this, including low population in an area due to overall climate, recent weather, unfortunate trap site selection, improper trap construction, or recent mosquito control activity.  We suspect that multiple explanations are at work here, and that mosquito spraying due to concerns about West Nile virus could have been a significant factor in these negative findings.

For extremes of location, the following participating groups deserve mention:

Northernmost:  Loyal WI and Clear Lake SD appear to be about the same.
Southernmost:  Largo FL
Westernmost:  El Paso TX
Easternmost:  Riverside RI

Special thanks to the following groups who have completed two years of participation:

Forty Fort PA (Hugh Hughes)
Riverdale MD (
Blacksburg VA (Mike Rosenzweig and SEEDS)
Hazard KY (Barbara Weaver)
Hammond IN (Jeannette Melcic, Frank M. Melcic, Kathy Stump)
Loyal WI (Barb Kingsbury)
Beach Park IL (Marie Gehrig, Judy Mobile)
Dahinda IL (Sharon Farquer)
Junction IL (Mark York)

The success of this project will depend critically on detecting changes in abundance through time, and for this we need persistence and continuity.  In addition to your students, we also thank any colleagues who might have gone unnamed in their efforts.

Plans for next year

We have learned a lot from our initial efforts, and have been able to use these preliminary findings to obtain support from the National Institutes of Health to fund the project for the next three years.  For this to succeed as a useful class exercise and as a research project, we need to overcome a few problems we have encountered along the way.  These include:

1.  The initial approach resulted in an overwhelming number of samples to process, and therefore a long time lag for return of results to you.  We spend hours and sometimes days processing too many samples from a single site, when a much smaller number of traps would tell us almost as much about that site.  We will reduce the number of traps to 25 per group.  The drawback is that it doesn't involve as many students individually as it did with the 1 trap per student method, but we think quicker feedback about the project will more than compensate.

2.  A large number of negative samples.  There is nothing inherently wrong with having a negative sample.  However, we know that some container-breeding mosquitoes are active in all of your communities, and a trap designed to be more attractive to mosquitoes will reduce the number of negatives.  Positive traps are certainly more interesting for your students.  Next time, we plan to use black containers that can be simply set on the ground next to a tree.  We wanted to use black all along, but couldn't find high quantities of black containers at an affordable price.  Reducing the number to send to each group will help a lot.

3.  Low participation rate, and low retention of groups from year to year.  We sent materials to 80 groups last summer, and only about 1/3 of them followed through.  As such, we estimate that we spent over $700 on postage and supplies that were not used.  The participation rate during the previous year was quite a bit higher, at about 2/3.  We think this relates to the additional work we asked of you last year (three weeks, changing liners twice) relative to 2003 (one week only).  Next year, we'll adjust this to a two-week sampling period with no change of liners.  A longer sampling period is preferred, to allow for fluctuations in weather.  However, if we lose participants then we're defeating our purpose, so this might be a good compromise.  The fall-off of participants from year to year is a serious problem for us to overcome, because the project really aims to look at change in populations through time. 

4.  Inconsistent trapping methods.  Some of the problem here related to us asking you to provide your own trap liners.  We will provide all materials this time, and the added simplicity of ground-resting traps should help.

Many thanks again to all who participated!  We hope to have you back again in 2005.